1. Field of the Invention
This invention relates to the construction of magnetic media read and write heads. More specifically, the invention relates to the construction of multi-layer tape head arrays having a narrow pitch.
2. Description of the Related Art
A typical tape head consists of an array of writers and readers dispositioned across a row fabricated by thin-film wafer technology. The separation between adjacent elements in an array has constraints. Consequently adjacent elements stretch across multiple tracks written in the tape. Read and Write access to all tracks is achieved by indexing the array across the tape.
One limitation on the separation between elements is to allow space for a wide coil on each write head. The width of the coil is constrained by magnetic requirements on the backgap size, number of turns and state-of-the-art coil photolithography. These limitation impose a separation much wider than the write track width and tape track pitch.
FIG. 1 is a top view of a typical write head array 100 of the prior art, with insulating layers transparent to aid in viewing relevant details. Tape or other magnetic media contacts the head array at the air bearing surface (ABS) 112. Write heads 102a-102c are located at a distance 122 from each other, which is about the width of five tracks in the example shown. Track position is determined by the center of write pole 110 of write head 102. Track location diagram 114 shows the location of tracks 116a-116c, which correspond to the write track locations of heads 102a-102c, respectively. Distance 122 is primarily determined by the width of backgap 106 in combination with the dimensions of coil 104. Yoke 108 returns the magnetic flux from write gap 110 to backgap 106.
FIG. 2 (prior art) is an air bearing surface (ABS) end view of tape head array 100 at section B-B in FIG. 1, with insulating layers 212 transparent to aid in viewing relevant details. Write heads 102a-102c are situated above shield layer 202 and insulating layer 204, respectively. Bottom pole layer 206 is situated above insulating layer and is common for all writes heads in the array. Bottom pole tip 208 is coupled to bottom pole layer 206. Upper pole tip 210 is separated from lower pole tip 208 by write gap 110. Upper pole tip 210 is coupled to yoke 108.
FIG. 3 (prior art) is a cross section view through section A-A of FIG. 2, with insulating layers transparent to aid in viewing relevant details.
U.S. Pat. No. 5,452,165 discloses a plurality of thin film magnetic heads which are arranged in a linear array with a spacing D between adjacent heads. The pole pieces of the magnetic heads are positioned in a side by side relationship in contrast to the normal pancake type of magnetic head. The linear array is angled at a skew angle theta with respect to the direction of travel of the magnetic medium. The track pitch is then D sin theta. The track width is substantially equal to the thickness of the pole tips P1T and P2T of the magnetic heads. This thickness can be in the order of 3 microns. With such a pole tip thickness the track pitch of each magnetic head in the linear array can be 3-4 microns. A plurality of narrow data tracks can then be provided with minimum pitch by a corresponding number of magnetic heads. The write signals are simultaneously fed to the heads or the read signals are simultaneously fed to the heads. This allows high data rates to be processed. The invention also provides different azimuth between adjacent heads to minimize cross talk between the tracks caused by track misregistration. Additional magnetic heads can be employed for servo control as needed.
U.S. Pat. No. 5,546,650 discloses a method of manufacturing a thin-film magnetic head having a write element capable of producing a magnetic flux density sufficient to write the high coercivity magnetic tapes at high track density. The manufacturing process requires a minimum number of lithographic steps, thereby increasing the yield of the multiple track magnetic head module. A trench is cut into the ferrite substrate material and filled with an insulator to produce a more efficient write element. A recess is then formed in the ferrite substrate having a geometry sufficient to hold a deposited thin-film conductive coil below the surface of the ferrite substrate. An insulator is then deposited on the ferrite substrate to form a gap spacer as well as to insulate the conductive thin-film coils from the ferrite substrate. The conductive thin-film coil is then deposited on the ferrite substrate in the recesses. A high-saturation flux density magnetic material is deposited on a planar nonmagnetic closure section and formed into separate magnetic pole pieces for each individual track. The magnetic pole pieces are then insulated from each other to produce a closure section having a planar surface matable with the ferrite substrate. The closure section is attached to the substrate by aligning the metal pole piece on the closure section. The magnetic pole piece is positioned in the front gap and has a width which defines the track width on the magnetic tape. The magnetic pole piece is also positioned to substantially cover the back gap region to increase the flux density existing at the front gap region.
U.S. Pat. No. 5,982,591 discloses integrated, juxtaposed head units of a magnetic head have transducing gaps directly adjacent a central plane transverse to the longitudinal direction of relative movement of a magnetic recording medium, adjacent transducing gaps being to opposite sides of the central plane. Head units adjoin each other so that a recording channel density of 100% is achieved. In one embodiment a common electrical conductor passes through a plurality of head units to one side of the central plane, and electrical connection tracks extending from a portion of the conductor form inductive transducing elements.
U.S. Pat. No. 6,650,496 discloses a matrix array of recording heads, wherein each head is independent from another both in terms of its magnetic circuit and excitation conductors. Each individual head has a planar magnetic circuit and an helical coil wrapped around the lower part of the magnetic circuit. The matrix array is collectively fabricated using full thin film technology on non-magnetic substrates. Preferably, the heads are aligned in an oblique lattice with the write gaps aligned along rows and offset by a constant value along columns. Each individual head is connected to the control electronics through interconnects to the backside of the wafer, allowing independent control of the write parameters. The die forming the device is shaped on its edges and top surface to optimize head/medium positioning and minimize wear.
U.S. Pat. No. 6,687,083 discloses a low profile inductive write head to improve track definition and head efficiency and to reduce overcoat and pole tip protrusion and cracking caused by thermal expansion. A first insulation layer of an insulation stack enclosing the coil layer is formed of an non-magnetic inorganic insulator material such as aluminum oxide,: silicon dioxide or titanium dioxide having a thickness of in the range of 0.2-0.3 microns. The thinner first insulation layer results in a significantly reduced slope of the insulation stack which decreases reflective notching during processing of the second pole tip to improve track definition. Improved thermal conduction properties of the inorganic insulator material improves heat sinking of the write coil reducing overcoat and pole tip protrusion and cracking at the pole tip/write gap layer interface.
U.S. Patent Application Publication 2002/0135918 A1 discloses a multi-magnetic recording head capable of increasing a magnetic recording density of information recorded on a magnetic recording medium. The multi-magnetic recording head includes a substrate, a pair of first thin film magnetic poles with a specific gap put therebetween, which are stacked over the substrate, and a pair of second thin film magnetic poles with a specific gap put therebetween, which are stacked over the pair of first thin film magnetic poles, wherein the pair of first thin film magnetic poles and the pair of second thin film magnetic poles are offset from each other in the direction nearly perpendicular to the stacking direction.
U.S. Patent Application Publication 2004/0066576 A1 discloses a magnetic write head having a vertically laminated back gap structure and method of making the same. The magnetic head is formed with lower and upper pole pieces and a back gap structure which connects the lower and the upper pole pieces in a back gap region. In one illustrative example, the back gap is a vertically laminated structure having alternating layers of magnetic and non-magnetic materials. Each alternating layer is perpendicular to both the lower and the upper pole pieces. This vertically laminated structure significantly reduces the eddy currents in the back gap region at high operating frequencies as the layers are oriented in a direction parallel with the magnetic flux.
U.S. Patent Application Publication 2002/0060879 A1 discloses a thin film magnetic head having a plurality of coils is capable of recording with higher density. A magnetic pole section for restricting a track width is formed between a lower core layer and an upper core layer, and two coil layers are tiered between a reference surface and a lower core layer through the intermediary of a coil insulating layer. This allows a magnetic path to be shortened. As a result, narrower tracks and lower inductance can be both achieved, and the narrower tracks combined with faster data transfer enable higher-density recording to be attained.
Head arrays of the prior art having a relatively large spacing can exhibit a number of disadvantages. One is the possibility of track misregistration (TMR), which is an alignment or registration error from the first track position (i.e. 116a) to the last track position (i.e. 116c) due to expansion or contraction of the magnetic media. Magnetic media, particularly tape, can expand or contract as a function of temperature or humidity. The magnitude of this error is dependent on the total distance between the first and last head positions in the array, therefore the further the heads are apart, the greater the registration error. Another disadvantage of a widely spaced head array is that data write times can be longer for a given media width and number of tracks. Closely spaced heads produce arrays having more heads per unit media width, and therefore more tracks can be written in parallel, increasing total data rates to the storage media. This may be of considerable importance in computer data back-up applications, where large hard drives need to be backed up on tape media.
In order to reduce adjacent head to head dimension 122, some designs in the prior art have used a staggered head positioning, requiring adjacent heads to be located on different levels (when viewed in the ABS view). This technique is advantageous in that the head spacing can be made as narrow as required without compressing coil structures or requiring state of the art lithography. This construction can result in higher production costs, however, since proportionately more layers have to be added during fabrication. This is particularly true when each head layer contains individual upper and lower pole layers. The structure is also more difficult to build due to the tendency of multiple layers to become non-planar as the stack gets thicker.
Of value would be an invention that allows a reduction of the spacing between the elements in the array while reducing the total number of layers in a staggered array. The usefulness of such an invention would be further enhanced if built with a process that incorporates planarization, so that thicker overall structures can be built with head spacings on the order of one track pitch.